Coated articles such as transparent shower doors and IG window units are often heat treated (HT), such as being thermally tempered, for safety and/or strengthening purposes. For example, coated glass substrates for use in shower door and/or window units are often heat treated at a high temperature(s) (e.g., at least about 580 degrees C., more typically from about 600-650 degrees C.) for purposes of tempering.
Diamond-like carbon (DLC) is sometimes known for its scratch resistant properties. For example, different types of DLC are discussed in the following U.S. Pat. Nos. 6,303,226; 6,303,225; 6,261,693; 6,338,901; 6,312,808; 6,280,834; 6,284,377; 6,335,086; 5,858,477; 5,635,245; 5,888,593; 5,135,808; 5,900,342; and 5,470,661, all of which are hereby incorporated herein by reference.
It would sometimes be desirable to provide a window unit or other glass article with a protective coating including DLC in order to protect it from scratches and the like. Unfortunately, DLC tends to oxidize and burn off at temperatures of from approximately 380 to 400 degrees C., as the heat treatment is typically conducted in an atmosphere including oxygen. Thus, it will be appreciated that DLC alone as a protective overcoat cannot withstand heat treatments (HT) at the extremely high temperatures described above which are often required in the manufacture of vehicle windows, IG window units, glass table tops, and/or the like.
Prior art FIG. 1 illustrates a conventional technique which is described in U.S. Pat. No. 8,071,166, the disclosure of which is hereby incorporated herein by reference. As shown in FIG. 1, prior to thermal tempering, a coated article includes a glass substrate 1, a DLC layer 11, a zinc oxide release layer 117a, and an aluminum nitride (e.g., AlN) oxygen barrier layer 17b. This coated article on the left side of FIG. 1 is then subjected to heat treatment (HT) such as thermal tempering, and the protective film 17 protects the DLC layer 11 during such heat treatment and prevents the DLC from completely burning off. Following the HT, the protective film 17 is removed using a liquid as described in the '166 patent.
Thus, DLC layer 11 is protected with a thermal barrier overcoat film 17 that protects the carbon based layer 11 from complete oxidation during tempering, with the protective film 17 thereafter being removed. Much of the protective overcoat 17 thickness consists of a cermet (ZnO—Zn) 117a, the rest being a dense dielectric of AlN 17b. 
It has been found that the cermet (ZnO—Zn; ZnOx) 117a has a high electrochemical potential compared to stoichiometric ZnO and is therefore thermodynamically metastable. The cermet is susceptible to humidity ingress and acts like a battery during sequences of high and low humidity/temperature. Over-extended grains of ZnO—Zn cermet are believed to create regions of high electrochemical potential which are readily attacked by water molecules to start an oxidative corrosion process of Zn to ZnO. To address these deficiency caused by the (ZnO—Zn; ZnOx) 117a, it has been attempted to further protect the protective film 17 with a thin polymer based flexible film (e.g., TPF), not shown, that can be peeled off. Moreover, it has also been found that the cermet has been problematic with respect to adhesion instabilities, and regarding causing burns in overlap areas where adjacent protective TPF films such as Novacel TPF 9047 overlap each other.
When the cermet (ZnO—Zn; ZnOx) 117a is about 160 nm thick for example, it has been found to have a rough surface with macroparticles sized at about 100 nm. Thus, for example, a 60 nm AlN layer 17b on top of the cermet 117a may not be thick enough to cover the cermet completely given the presence of such macroparticles. It is believed that the problems discussed above, including a significantly chemically active surface of the protective coating, is/are caused at least in part by the cermet 117a not being fully oxidized ZnO. The prior art stack in FIG. 1 has deficiencies including (i) being inhomogeneous and based on a bi-phasal matrix of ZnO—Zn, and (ii) the presence of large macrograins of ZnO/Zn in the matrix which can result in the top AlN not conforming to the release layer and allows water vapor molecules to reach the ZnO—Zn layer before and/or during HT. These two deficiencies, in combination, give rise to the instability of the overcoat 17 and its susceptibility to humidity even in the presence of further protective TPF.
In certain example embodiments of this invention, it has been found that one or more of the above problems can be solved and/or addressed by introducing significant amounts of nitrogen (N) into the zinc oxide inclusive release layer, so that the release layer is of or including zinc oxynitride (e.g., ZnOxNz). This allows the thermal barrier stack to be electrochemically substantially inactive prior to and/or during heat treatment such as thermal tempering. The phase of the release layer is substantially homogenized by introducing N in such a manner so as to produce a substantially uniform phase of zinc oxynitride. This helps stabilize the matrix, using control of the nitrogen to oxygen ratio in the release layer itself and/or during its deposition. The improved release layer is advantageous in that (i) the protective coating now has a higher degree of electrochemical homogeneity—lower chemical gradient within film, (ii) smoother release layers and protective films can be realized, and/or (iii) nitrogen atoms passivate the ZnO in the release layer and provide a more chemically stable interface with the barrier layer (e.g., AlN). Advantageously, the protective film can remain substantially stable throughout the sequence of environments that the layer stack is exposed to, including transportation and storage prior to and during HT such as thermal tempering.
In certain example embodiments of this invention, there is provided a method of making a heat treated coated article, the method comprising: heat treating a coated glass substrate, the coated glass substrate comprising, prior to the heat treating, a glass substrate, a layer comprising carbon (e.g., DLC) on the glass substrate, and a protective film on the glass substrate over at least the layer comprising carbon, wherein the protective film includes a release layer and an oxygen barrier layer, wherein the release layer comprises or consists essentially of zinc oxynitride ZnOxNz, and where a nitrogen to oxygen ratio z/x in the release layer is at least 0.40 or at least 0.55; during said heat treating of the coated glass substrate with the layer comprising carbon and the protective film thereon, the protective film prevents significant burnoff of the layer comprising carbon, and wherein the heat treating comprises heating the glass substrate to temperature(s) sufficient for thermal tempering, heat strengthening, and/or heat bending; and removing (e.g., using a removing liquid(s)) at least part of the protective film during and/or after said heat treating. In certain example embodiments of this invention, the release layer is a dielectric layer. In certain example embodiments, measured on an atomic basis, the nitrogen to oxygen ratio z/x in the ZnOxNz based release layer is from 0.40 to 1.2, more preferably from 0.55 to 1.2, more preferably from about 0.55 to 1.0, even more preferably from about 0.60 to 0.85, and most preferably from about 0.63 to 0.80.
In certain example embodiments of this invention, there is provided a method of making a heat treated coated article, the method comprising: heat treating a coated glass substrate, the coated glass substrate comprising, prior to the heat treating, a glass substrate, a layer comprising carbon on the glass substrate, and a protective film on the glass substrate over at least the layer comprising carbon, wherein the protective film includes a release layer and an oxygen barrier layer, wherein the release layer comprises zinc oxynitride ZnOxNz and where at least one of: (i) a nitrogen to oxygen ratio z/x in the release layer is at least 0.40, and/or (ii) a ratio of nitrogen gas to oxygen gas during sputtering in an atmosphere in which the release layer is sputter-deposited is at least 0.40; during said heat treating of the coated glass substrate with the layer comprising carbon and the protective film thereon, the protective film prevents significant burnoff of the layer comprising carbon, and wherein the heat treating comprises heating the glass substrate to temperature(s) sufficient for thermal tempering, heat strengthening, and/or heat bending; and removing at least part of the protective film during and/or after said heat treating